1. Field of the Invention
The present invention relates to a laser beam optical axis adjusting mechanism in a particle size distribution measuring apparatus which is furnished with a light source for irradiating a laser beam onto a sample and an optical detector for receiving the scattered light irradiated on the sample to measure the particle size distribution of the sample based on the intensity pattern of the light scattered over the sample and more particularly to an adjustable mirror to enable a simple and compact design.
2. Description of Related Art
A conventional particle size distribution apparatus for example, as shown in FIG. 12, includes a laser light source for generating a laser beam 71, a condenser lens 72, a cell 73 for accommodating the sample 74, and a light detector 75 for receiving the light scattered by irradiation on the sample 74. The light detector 75 is designed to measure the particle size distribution of the sample based on the intensity pattern of the light which has been scattered as it passes through the sample.
In the particle size distribution apparatus described above, obtaining an accurate coincidence of an optical axis of the laser beam with a center of the optical detector 75 is important in measuring the particle size of the sample to any acceptable level of precision. The optical axis of a laser beam can be offset from the center of the optical detector 75 due, for example, to thermal stress of the laser light source 71, thermal stress of the bench base (illustration omitted) that is provided with the cell 73, the condenser lens 73 and the optical detector 75 or the like, or due to a change of the mounting position at the time of the replacement of the cell 73. It is a general practice that the optical axis adjustment is generally performed on each occasion of measurement of the particle size.
To cope with the above situation, though illustration is omitted, there has been a practice to provide four light receiving elements such as photo-diodes at a central part of the optical detector 75, and, prior to the measurement, to align the optical axis by moving the optical detector 75 in the directions of X and Y axes so as to make the size of the intensity signals outputted from the four light receiving elements equal.
In order to move the optical detector 75 in the direction of the X and Y axes, ordinarily there are used two separate actuators 76, 77 such as a piezoelectric element, stepping motor, etc. The optical detector 75 is called a ring detector or a light receiving element comprising a plurality of photodiodes formed in an arc shape and arrayed in a sector configuration on the plate surface to form a large plate-like member. The optical detector 75 is at a position on the furthest side of the cell 73 and distant from the laser light source 71. For this reason, in order to secure a sufficient shift amount necessary for making an optical axis adjustment, a large space is required to be provided in the apparatus, with the consequence of a large size requirement for the optical axis adjusting mechanism, a complexity of construction, and an alignment requirement of a high cost.
The prior art is still seeking improvements in this field including requirements to render the measurement apparatus in a compact configuration.
The prevent invention provides a laser optical axis adjusting mechanism having a simple and compact construction at low cost, with an entirely unique style of optical axis adjustment from that of conventional systems.
In order to attain the above objects, the present invention is characterized by providing the laser beam optical axis adjusting mechanism with a mirror member for reflecting light irradiated from the laser light source and directing it towards an optical detector, an actuator unit for changing an angle of the mirror surface around an axial axis in two-dimensional directions, and an actuator controlling unit for bringing the optical axis of the laser beam which is reflected on the mirror face into agreement with a center and of the above optical detector. The actuator unit can include a support base for the mirror member and a pair of actuator members for moving the support base in two dimensions. The support base can be mounted with a universal coupling and each actuator member can include lever members that are integrally connected to a support structure with L-shaped slits.
The optical axis of the laser beam can be significantly modified in angle by a slight angular change of the mirror position, and since the change of the mirror angle for optical axis alignment can be satisfied by only a small amount of movement, especially the nearer the mirror is positioned to the laser light source, a small mirror is effective for reflecting the laser beam. Accordingly, it is possible to constitute the entire optical axis adjusting mechanism including the actuator, at a low cost, and in a compact design.